1. Field of the Invention
This invention relates to a method of producing olefin oligomers and hydrogenation products thereof. More particularly, the invention relates to a method of producing olefin oligomers or hydrogenation products thereof, which comprises feeding to the polymerization system (i) at least one alpha-olefin having a terminal vinyl group and containing 6 to 14 carbon atoms, (ii) isobutylene and/or diisobutylene, and optionally (iii) 1-butene so that the conditions ##EQU1## wherein a is the number of moles of the alpha-olefin having a terminal vinyl group and containing 6 to 14 carbon atoms as fed to the polymerization system, b is the number of moles of isobutylene as fed to the polymerization system, c is the number of moles of diisobutylene as fed to the polymerization system and d is the number of moles of 1-butene as fed to the polymerization system, may be satisfied, while carrying out the polymerization in the presence of an aluminum halide catalyst, and optionally hydrogenating the resulting polymer.
2. Description of the Prior Art
Liquid oligomers produced from alpha-olefins each having a terminal vinyl group and containing 6 to 14 carbon atoms (such olefins hereinafter called "higher alpha-olefins"), and especially hydrogenation products thereof, thanks to their characteristic properties, are the objects of attention in respect of their use as synthetic lubricants, base oils for cosmetics and so on. The so far known methods of producing higher alpha-olefin oligomers include thermally or peroxide-initiated radical polymerization, coordinative anionic polymerization using a Ziegler catalyst (Journal of Applied Chemistry 12, 33-45(1962)), and cationic polymerization using a Lewis acid, such as boron trifluoride or an aluminum halide (U.S. Pat. No. 3,149,178), said Lewis acid being optionally modified with a ketone, an ester, an ether, an alcohol or the like (U.S. Pat. No. 3,953,361 and U.S. Pat. No. 3,952,071). Considering yield, difficulty or ease in polymerization degree regulation, breadth of molecular weight distribution, viscosity characteristics of product polymer, difficulty or ease in catalyst handling and removal and other factors collectively, those methods that employ a modified Lewis acid, especially a modified aluminum halide, as catalyst are regarded to be most advantageous among said known methods. Although aluminum halide catalysts are very preferable in view of price and easiness in handling and in other respects, polymerization of higher alpha-olefins in the presence of an aluminum halide generally tends to result in unnecessarily high polymerization degree and relatively broad molecular weight distribution. In order to overcome these disadvantages, methods using modified aluminum halide catalysts are under evaluation. However, modification of an aluminum halide with modifiers such as mentioned above causes considerable decrease in rate of polymerization of higher alpha-olefins, hence a greater amount of catalyst, a longer polymerization time and a higher polymerization temperature are required, and, as a result, the products are often of an inferior quality, containing coloring impurities, for example.
3. Detailed Description of the Invention
The present inventors have endeavored diligently to solve the above problems and produce more advantageously on a commercial scale liquid hydrocarbons useful as lubricants and base oils for cosmetics by olefin oligomerization, and have now found that a high polymerization rate results, the molecular weight of the product polymer can easily be regulated and hydrogenation of the polymerization products can be carried out effectively, if higher alpha-olefins are copolymerized with a specified amount of at least one vinylidene-type olefin selected from the group consisting of isobutylene and diisobutylene (the olefin as just defined being hereinafter called "vinylidene-type olefin" for short) or a mixture of at least one vinylidene-type olefin and 1-butene, said 1-butene also being present in a specified amount, in the presence of an aluminum halide catalyst. Thus, according to the present invention, oligomers or hydrogenation products thereof narrow in molecular weight distribution and comparable in viscosity-temperature relationship and low temperature properties to those obtained by prior art polymerization of higher alpha-olefins alone in the presence of a modified aluminum halide catalyst are produced in good yields. The hydrogenation products from the olefin oligomers produced by the method in accordance with the invention are superior in oxidation stability, especially at high temperatures, to the hydrogenation products from oligomers of higher alpha-olefins alone.
The higher alpha-olefins to be used according to the invention are, for example, 1-hexene, 4-methylpentene-1, 1-octene, 1-decene, 1-dodecene and 1-tetradecene. These higher alpha-olefins may be used each individually or in the form of a mixture of two or more of these in an arbitrary ratio. These higher alpha-olefins may contain internal olefins such as 2-pentene, 2-octene, 2-decene, 3-dodecene and so on in such amounts as have no substantial adverse effects. 1-Butene and/or the vinylidene-type olefins may also contain internal olefins such as 2-butene and so on in such amounts as have no substantial adverse effects.
According to the invention, it is important, in order to produce olefin oligomers with favorable properties at a high polymerization rate and in good yield, to feed higher alpha-olefins, vinylidene-type olefins and optionally 1-butene to the polymerization system so that the following conditions may be satisfied: ##EQU2## where a, b, c and d are the numbers of moles of higher alpha-olefins, isobutylene, diisobutylene and 1-butene fed to the polymerization system, respectively. When the ratio (b+2c+d)/a is less than 0.25, the polymerization rate is low, the viscosity of the product is too high and the molecular weight distribution is broad, and moreover the hydrogenation product will not show substantially excellent oxidation stability, that is one feature of the invention. When, on the other hand, the ratio (b+2c+d)/a is greater than 4, the polymer yield after cutting off low-boiling fractions is not good and the viscosity index of the product polymer is low. If d/(b+2c) is greater than 2.5, the viscosity of the product polymer will be too high. In case d/a is greater than 2.5, the polymerization rate will be low, and the product will have an unnecessarily high polymerization degree, a low viscosity index value, a high viscosity and a high pour point. It is especially preferred that (b+2c+d)/a is from 0.5 to 3 and/(b+2c) is from 0 to 2.0, while the above condition (3) is satisfied. By altering the ratio d/(b+2c) in the range of 0 to 2.5, preferably in the range of 0 to 2.0, it is possible to control or regulate the molecular weight of the product polymer to some extent in a certain range. As understandable from the previous description, increase in the ratio d/(b+2c) favors molecular weight increase, while decrease in the ratio d/(b+2c) favors decrease in molecular weight. Although, in the polymerization according to the invention, the total amount of each olefin may be charged into the polymerization system all at once prior to the initiation of the polymerization, it is preferred to carry out the polymerization while feeding each olefin continuously or intermittently to the region where an aluminum halide catalyst is present and where the polymerization is going on, whereby it is possible to copolymerize a vinylidene-type olefin or a vinylidene-type olefin plus 1-butene with higher alpha-olefins especially effectively and bring about a sharper molecular weight distribution of the product polymer and besides removal of polymerization heat becomes easy.
Examples of the aluminum halide catalyst to be used in accordance with the invention are aluminum chloride, aluminum bromide, aluminum iodide and aluminum fluoride. If desired, by using in place of an aluminum halide itself a compound capable of forming an aluminum halide, it is possible to make the aluminum halide in situ. Thus, for example, a reaction mixture obtained by reacting an organoaluminum compound, such as triethylaluminum or diethylaluminum chloride, with a large excess (usually in an atomic ratio Ti/Al of from 2 to 10) of a titanium halide may be used as catalyst. Further, if desired, the aluminum halide may be modified with a variety of so-far known modifiers such as esters, ketones, alcohols and ethers. According to the invention, the polymerization with modified aluminum halide catalysts also proceeds smoothly, and it is possible to substantially decrease the amount of catalyst or shorten the polymerization time as compared with the prior art cases where higher alpha-olefins are polymerized with modified aluminum halide catalysts but with no addition of vinylidene-type olefins. Although various aluminum halide catalysts can be used as above mentioned, preferred catalysts are unmodified aluminum halides and modified aluminum chloride, and among these, unmodified aluminum chloride is most preferred in respect of catalytic activity and from cost considerations.
Desirably, the polymerization according to the invention is carried out at a temperature in the range between about 20.degree. C. and about 120.degree. C. A polymerization temperature in the range of from about 40.degree. C. to about 100.degree. C. is especially recommendable. Too low temperatures tend to cause not only heavy expenses for removal of polymerization heat but also decrease in effects of the addition of vinylidene-type olefins and as a result excessively high polymerization degrees. On the other hand, polymerization at an unnecessarily high temperature results in increase in the acid number of the reaction mixture, marked coloration of the product and decreased yield of the polymer after cutting off low-boiling fractions. The amount of the aluminum halide catalyst is preferably about 0.1 to 5 mole % based on the total monomer amount to be charged. It is preferred in commercial production to carry out the polymerization with continuous or intermittent addition of the catalyst to the polymerization system.
The polymerization may be carried out without any solvent. However, the presence of a solvent is preferable, because it lowers the viscosity of the solution and besides facilitates separation of the product from the catalyst after the reaction. Preferable solvents for the polymerization are, for example, butane, pentane, hexane, heptane, isooctane, cyclohexane, and other saturated aliphatic or alicyclic hydrocarbons. Though the amount of the solvent is not especially limited, generally it is used in an amount about 0.2 to 4 times (by volume) the total amount of monomers to be charged. In a preferred industrial embodiment of the invention, the polymerization is carried out in the copresence of an appropriate amount of a metal capable of capturing a hydrogen halide possibly formed by the action of a trace amount of water present in the polymerization system, such as aluminum, zinc, tin or lead.
After completion of the polymerization, the catalyst component is removed from the reaction mixture by filtration or centrifugation. The filtrate or liquid after the removal of the catalyst is washed with water and/or a dilute, aqueous alkali solution, the unreacted monomers and the solvent are then distilled off, and if necessary, low-boiling fractions are removed from the remaining liquid under reduced pressure. There is thus obtained a colorless to pale yellow liquid polymer. This liquid polymer as recovered from the polymerization mixture is per se useful, for example, as a synthetic lubricant. It is preferable, however, to hydrogenate said liquid polymer in order to improve its thermal and oxidation stability. In said hydrogenation, a trace amount of a halogen originating from the catalyst and unavoidably contaminating the liquid polymer after the polymerization acts as an inhibitor or poison to the hydrogenation catalyst, shortening the life thereof. It has been found by the present inventors that the life of the hydrogenation catalyst can be lengthened when the hydrogenation is carried out after washing the liquid polymer with water and/or a dilute, aqueous alkali solution and then bringing the polymer so washed into contact with an inorganic adsorbent so that the transmittance of the polymer as measured at 400 nm is not less than 0.98. The liquid polymer to be brought into contact with the inorganic adsorbent may be in the form of a solution in an appropriate solvent or in the solvent-free state. Preferably, the polymer as obtained after the removal of the AlCl.sub.3 -oligomer complexes from the polymerization mixture is first washed with dilute aqueous solution and then with water, and thereafter treated with the adsorbent. Improvement of the transmittance of the polymer by this treatment up to 0.98 or above means that the halogen capable of deactivating the hydrogenation catalyst has been removed to a satisfactory extent. The transmittance mentioned above is herein defined as the ratio of the intensity of the light transmitted by a liquid polymer specimen after removal of the solvent by distillation if the solvent is contained, which specimen has been taken from the liquid polymer after the treatment with the inorganic adsorbent, to the intensity of the incident beam with a wavelength of 400 nm, the cell thickness being 1 cm.
The inorganic adsorbent suitable for achieving the above purpose is selected from among silica, silica-alumina, alumina, zeolite, diatomaceous earth, bentonite and activated clay. A mixture of two or more of these inorganic/adsorbents may also be used. The inorganic adsorbent may be in the form of a powder or be molded into granules, rods, tablets or any other appropriate form. Among these inorganic adsorbents, activated clay in the form of a powder is especially preferred in consideration of price, activity and other factors important from the commercial point of view. Contact of the liquid polymer with the inorganic adsorbent can be realized, depending upon the form of the adsorbent, by stirring a mixture of these or by allowing the polymer to pass through an adsorbent column, after adjusting the viscosity of the liquid properly, in dependence of the viscosity of the olefin polymer, by altering the temperature or by diluting with an aliphatic hydrocarbon. Generally, the amount of the inorganic adsorbent is from 1 to 20% by weight based on the liquid polymer, said amount depending on the kind of the inorganic adsorbent, for instance.
The hydrogenation can be carried out employing the methods and conditions known per se. Thus, for example, the above-mentioned liquid polymer may be brought into contact with hydrogen at a hydrogen pressure of about 2 to about 100 atmospheres and at a temperature of about 50.degree. to about 200.degree. C., in the presence of about 0.1 to 10% by weight based on said liquid polymer of a hydrogenation catalyst (e.g. Raney nickel, nickel on diatomaceous earth, palladium on carbon, palladium on silica, palladium on alumina) in the presence or absence of a solvent. Solvents of the same kinds usable in the polymerization mentioned above may serve also as solvents in the hydrogenation. The olefin oligomers produced by the polymerization in accordance with the present invention have properties suitable for said hydrogenation, and consequently said hydrogenation is carried out effectively. After the hydrogenation, high performance liquid hydrocarbons (hydrogenated olefin oligomers) can be obtained by removing the hydrogenation catalyst and the solvent (if present) in a conventional manner, if necessary followed by removing low-boiling fractions. Generally, the olefin oligomers and the hydrogenation products therefrom produced by the method of the invention contain hydrocarbons of 25 to 45 carbon atoms as main components, and show a pour point (according to JIS K-2269) of about -30.degree. C. or below, a viscosity at 100.degree. F. (according to JIS K-2283) of about 20 to about 150 cSt (centistokes), a viscosity at 210.degree. F. (according to JIS K-2283) of about 4 to about 15 cSt, and a viscosity index (VI, according to JIS K-2284) of about 80 to about 130. The relationship between the average molecular weight and the properties can approximately be seen in Table 1 for a few typical examples. Whereas Table 1 contains the data only for hydrogenated olefin oligomers, the corresponding olefin oligomers before hydrogenation possess almost the same properties.
Table 1 __________________________________________________________________________ Average molecular Viscosity at Viscosity Pour point weight* 100.degree. F. (cSt) 210.degree. F. (cSt) index (VI) (.degree.C.) __________________________________________________________________________ ca 400- 500 ca 20- 55 ca 5- 7 ca 90- 120 ca -45 or below ca 550- 650 ca 40- 100 ca 7- 11 ca 95- 120 ca -40 or below ca 650- 700 ca 70- 130 ca 10- 13 ca 100- 130 ca -30 or below __________________________________________________________________________ *estimated by gel permeation chromatography (GPC)
The present invention that has made it possible to produce such liquid hydrocarbons with balanced, excellent properties as mentioned above easily and at low costs by oligomerization of olefins is of a great significance from the commercial viewpoint.